Generator sets for use on building sites are already known and comprise a frame carrying an electric generator and an internal combustion engine for driving the generator, the latter being designed to supply single-phase and/or three-phase alternating current at the voltage and frequency of the local mains supply.
On building sites, in addition to the machines that are designed to be supplied with three-phase or single-phase electric current form the local mains supply, there are certain machines, such as vibrating needles for concrete, concrete vibrators, pneumatic drills, etc., which have to be supplied with a special current usually a single-phase or three-phase current of 42 V at a frequency of 200 Hz. In order to provide this special current, contractors use another generator set comprising a petrol engine or a diesel engine which drives a generator designed to provide this current.
The aim of the invention is to reduce expenditure on equipment and to offer greater versatility, especially in the case of concrete works, by simultaneously permitting the use of the various machines necessary for carrying out these works, i.e. vibrating needles, mechanical trowels, vibrating beams, cement mixers, lighting, etc.